1. Field of the Invention
This invention relates to a one-piece plastic snap-hinge closure, having a lower part and a cap hingedly connected thereto, the cap and the lower part each having a jacket wall which, in the closed position of the closure, are located vertically flush above each other and are connected to each other by at least one film hinge located in their plane of separation, and having two spring elements, integrated into the jacket walls of the two parts, which generate the snap action.
2. Description of the Prior Art
The three most important points for the commercial success of a plastic closure are functionality, ease of manufacturing and aesthetic appearance. A fourth point is the price, which is always important. However, there are hardly any large differences, as far as one-piece closures are concerned, which can be manufactured without sliders in extrusion molds.
Functionality includes two essential criteria, namely closeness, the most essential function of any closure, and the snap action, a characteristic of a snap closure. Today, every snap closure achieves the required closeness, but the snap action varies considerably with different closures. This is obvious once it has been realized how complex the interaction of the different forces is and how this is affected by the geometry of the closure and its hinge.
The force for generating the snap action is always created by bending elasticity. Accordingly, it is possible to utilize a spring element or to design the geometry of the closure such that spring action results from elastic deformation of parts of the closure. The first variant, operating with spring elements, has been known for many years and employs a toggle joint as the spring element. The second variant employs so-called strap retainers which connect the cap and the lower part to each other, and at least one interposed film hinge, by which the two parts are pivotably connected to each other.